You need a password to change anything from main mod - as far as i know. You can protect your mods by password.
The main mod paths have hardcoded protections in the editor so it won't allow you to open anything for editing in the paths \Data\Public\Main, \Data\Public\Game, \Data\Mods\Main.
To edit them do right click -> Copy to my module ... on the resource, it makes them editable (another "fix" for this is hex editing the editor DLLs, though this is not recommended).
The annoying thing is that the original material scripts are not included in the game at all, only the compiled shaders, so you cannot really open any of the materials in the game
